Single cam on camshaft is suitable for reversing of 2/S, large bore engine. But not suitable for 4/S engine, because reversing of 4/S engine requires turning of Inlet Valve cam, Exhaust Valve cam, Fuel cam and arrangement for Starting air Distributor, with their correct timings.

Double cam on camshaft, is moved axially by means of servo system or manual system, so that all cams get their correct timings, in 4/S engine. (Used also for 2/S).

Lost motion:

Angular period between TDC points for Ahead and Astern running will be the “lost motion” required for Astern running.

When reversing 2/S, exhaust ported engine, both Fuel Injection timing and Air Starting timing must be changed.

Retiming is carried out by altering camshaft position radially, relative to crankshaft. This is called “lost motion” of camshaft.

Why ‘lost motion’ necessary on some engine?

Some 2/S, large bore, exhaust ported engines are Direct Reversing.

Both Fuel Injection timing and Air Starting timing must be changed.

Camshaft has single cam

Retiming is carried out by altering camshaft position radially, (not axially), relative to crankshaft, by means of servo system.

Why ‘lost motion’ not necessary on some engine?

Some 2/S and 4/S engines are Direct Reversing.

Inlet Valve cam, Exhaust Valve cam, Fuel cam and arrangement for Starting air Distributor, with their correct timings, must be changed.

Camshaft has double cam

Retiming is carried out by altering camshaft position axially, from Ahead cams to Astern cams, by means of servo and manual systems.

Lost Motion Camshaft:

When reversing 2/S Exhaust Ported Engine, both Fuel Injection and Air Starting timings must be changed.

Lost Motion Clutch cam design can be used to alter reversing direction.

Camshaft position is altered radially relative to crankshaft.

Same cam is used for ahead and astern running.

Reversing Servomotor, operated by Engine Reversing Controls, is fitted to camshaft drive mechanism to do this.

Camshaft will lose motion or be retarded, through required angle (about 98°) by oil operated Lost Motion Clutch, causing the Reversing Servomotor to rotate the camshaft.

Fuel Pump cam and Air Start cam will now operate the Engine in reversed direction.

Lost motion is carried out while the Engine is at rest.

For Uniflow Scavenge Engine, the second Servomotor is fitted to Exhaust Valve drive.

Safety springs, fitted in main servo, push the servo piston forward, to allow propeller pitch to full ahead position, in the event of hydraulic system failure. The springs are powerful enough to overcome friction, but RPM of 70% maximum should not be exceeded.

Telemotor system failure:

Hand-operated control valve is used, in the event of telemotor failure.

Main hub servo failure:

If main servo fails, the system has either Emergency Servo or Mechanical Link.

CPP Bridge Control:

CPP in large vessels are usually fitted with Combinator Control on the Bridge.

A single lever controlling both propeller pitch and engine speed, either through pneumatic or electronic means.

In either case, closed loop circuits are employed, so that feedback of propeller position and engine speed, balance off the control signal.

In electronic control system, ME load is kept at desired value, by automatically changing the propeller pitch, irrespective of variation in external conditions; e.g. change in resistance in propulsion caused by wind and sea.

Main panel receives, converts and transmits signals, and a potentiometer for adjusting ME load, and an instrument showing fuel pump setting, is provided.

Control panel on Bridge contains instrumentation corresponding to that of Main panel.